finish

got my lathe working properly now however I am not happy with the finish I am getting I am using hss they are ground correctly get a fairly good finish on ally but I made a valve guide drift today out of re bar and the finish is like an old record I tried different speeds oil but didn't seem to make much difference I don't know why I am not getting a nice finish

Rebar both plain round and HT is rather gummy nasty stuff to machine get a nice bit of free cutting mild steel and try again.

You also say "they are ground correctly" was that teh same tool for both materials? as the steel one ideally should have less top rake than the one for ali

Edited By JasonB on 28/04/2015 20:18:29

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When I first got my lathe I was struggling to get anything other than as you put it a record finish. Even after spending eons with every speed and feed rate available. I also spent considerable time grinding what I considered to be 'perfect' HSS tools - So much so that I convinced myself that the head stock bearings in the lathe were shot.

I asked a friend of mine who has been a pro for over 40 years could he come and cast his experienced eye over my useless defunct piece of scrap iron that had the audacity to be called a lathe.

He had a quick look at the bits of steel I had butchered then turned his attention to the tool bit. There was a pronounced 'Mmmmmmmmm" Did not say anything else but looked at me with slightly raised eyebrows in a somehow sympathetic way one would look at an injured puppy.

A few seconds, a few flicks of his wrist with tool at the grinder and back into the lathe it went at the correct height. The scrap iron of a machine was switched on and magically started to produce great swathes of swarf with a far deeper cut than I would have dreamed of taking. ............ The finish on the bar was fantastic. He went even deeper still and the swarf became streaming ribbons but still with a fantastic finish on the bar.

Then followed a lesson on tool grinding. (which I am still useless at) He also added that it would not be a good idea for me to take cuts as deep and as fast on regular basis with it being such a small machine. But he did so only to prove to me that there was nothing at all wrong with the headstock bearings and the machine was basically sound.

I was convinced that my grinding was correct and I had bought a lemon of a machine. .................. Incorrectly.! ........... And 40 plus years experience showed within a very short time how incorrect I was.

Nick

My first attempts looked like were done with a 6 inch nail. As said already the type of steel makes a difference. Also important to put a radius on the tool tip - a sharp point is not good for finish. Try going in at a flatter angle or even a radiused tool. In the end a rough job can be made to look better using the file and a moderate speed - be careful though.

As mention by Jason, rebar has got to be one of the nastiest 'metals' to machine, and only useful for concrete.

Even welding the stuff would be a nightmare I would think, as who knows what the ingredients are.

Tried rebar once but consigned it to the 'Never Use Again' list.

Geoff - Sometimes I DO learn I would let you all know

Stick with HSS. A lot of newbies think it is the tool and get suckered into a cheap set of a dozen carbide tipped tools which turn out even worse. Also no need to go for inserts on a small lathe like yours.
There is plenty of stuff on the web and in books about tool grinding but it is all too easy to get intimidated by it and all fussed about angles.

You have seen the basic 'knife' tool shape. It has 3 angles. Make each of them 10 degrees, round off the point, and that is fine for steel and ok for everything else. Sometime you can make one with a bigger slope on the top face for aluminium and another with a flatter top for brass. It is not difficult so don't be put off. Falling off logs is difficult.

thanks guys I will keep at it

One thing you should know is that Tipped tooling needs to run at 150% faster than HSS, no fine cuts but load the tool with a good cut and then tipped tools will work! For general work HSS ground correctly will do what ever you want.

Clive

falling off logs....I don't get it?

Interesting discussion and really gets me thinking about the machining I've been doing using scrap round section of all and any unknown origin. Exception has been stainless. I chucked a piece of scrap 1/2" round the other day and marvelled and the finish and ease of parting off so I assume this be of teh free turning variety. It's got me now searching for a supplier in Au who has a selection of sizes and sells at less than tonne lots. Can any reader assist? A few calls to some local suppliers result in stunned silence when enquired about free cutting steel.

Cheers, Andrew

For idiot proof HSS tooling I can recommend the pre-formed HSS tools. They work well on steel and it ought to tell you once and for all whether your tools are ground correctly.

**LINK**

A bit more than blank toolbits and shaping your own but they just need touching up on a diamond hone to get them to cut well.

HTH

Jon

I use a tangential tool for the majority of my machining that use a 1/4" square tool bit; I do have a 7 piece set of HSS tools from one of the ME tool suppliers...usual disclaimer...

http://chronos.ltd.uk/acatalog/info_HS10S_.html

plus a few indexible tip tools that are used occasionally so I'm pretty well covered for all types of material, but to reiterate, the tangential takes preference, sharpened using the provided guide but with the addition of a small radius on the corner, honed on after sharpening, the finish is quite satisfactory for general finishing.

George.

Edited By mechman48 on 30/04/2015 13:31:21

Like George I use a tangential tool holder for most of my work and I get a really good finish both turning and facing. Mine was from eccentric engineering and works very well.

At first I bought myself a selection of insert cutters thinking these would cater for all my needs having seen them in action in work but I just could not get the finish I wanted on aluminium and mild steel. I was limited to 2000rpm on the spindle of my lathe and after discussing my requirements with a insert supplier and trying a few different types it was concluded that at this spindle speed the inserts were not going to perform at their best. I subsequently sold my insert holders and ground a number of HSS tools. Knife tools both left and right hand are extremely useful!

Having said that, whilst machining the cast iron castings on the Stuart 7A a couple of the castings had very hard spots in them which quickly rendered my HSS tools useless. A borrowed an insert cutter which quickly made a perfect job of machining the castings so guess what...I have replaced the ones I sold

Gathering up some 1/4 square HSS from "home and workshop" and trawling the internet for guides on grinding lathe tools (which there are many!) has significantly improved the quality and accuracy of the parts I have made so far.